Activation of K_Ca3.1 by SKA‐31 induces arteriolar dilatation and lowers blood pressure in normo‐ and hypertensive connexin40‐deficient mice

Abstract

BACKGROUND AND PURPOSEThe calcium-activated potassium channel KCa3.1 is expressed in the vascular endothelium where its activation causes endothelial hyperpolarization and initiates endothelium-derived hyperpolarization (EDH)-dependent dilatation. Here, we investigated whether pharmacological activation of KCa3.1 dilates skeletal muscle arterioles and whether myoendothelial gap junctions formed by connexin40 (Cx40) are required for EDH-type dilatations and pressure depressor responses in vivo. EXPERIMENTAL APPROACHWe performed intravital microscopy in the cremaster muscle microcirculation and blood pressure telemetry in Cx40-deficient mice. KEY RESULTSIn wild-type mice, the KCa3.1-activator SKA-31 induced pronounced concentration-dependent arteriolar EDH-type dilatations, amounting to ∼40% of maximal dilatation, and enhanced the effects of ACh. These responses were absent in mice devoid of KCa3.1 channels. In contrast, SKA-31-induced dilatations were not attenuated in mice with endothelial cells deficient in Cx40 ) decreased arterial pressure by ∼32 mmHg in all genotypes. The depressor response to 100 mg·kg −1 SKA-31 was associated with a decrease in heart rate. CONCLUSIONS AND IMPLICATIONSWe conclude that endothelial hyperpolarization evoked by pharmacological activation of KCa3.1 channels induces EDH-type arteriolar dilatations that are independent of endothelial Cx40 and Cx40-containing myoendothelial gap junctions. As SKA-31 reduced blood pressure in hypertensive Cx40-deficient mice, KCa3.1 activators may be useful drugs for severe treatment-resistant hypertension. AbbreviationsCx40, connexin40; DP, diastolic pressure; EDH, endothelium-derived hyperpolarization; KCa, Ca

New Positive Ca2+-Activated K+ Channel Gating Modulators with Selectivity for KCa3.1

“…In mice, SKA-31 doses of 10-30 mg/kg have been reported to lower blood pressure more prolonged (∼30 mmHg) for 60-90 minutes) (Sankaranarayanan et al, 2009;Köhler, 2012). Significant blood pressure-lowering effects with SKA-31 doses of 30 mg/kg have been further observed in models of hypertension like angiotensin II-infused (Sankaranarayanan et al, 2009) and connexin 40-deficient mice (Radtke et al, 2013), which exhibit severe chronic renindependent hypertension. However, the responses typically lasted only about 1 hour.…”

“…Since both K Ca 3.1 and K Ca 2.3 are expressed in vascular endothelium and have been shown to be involved in the so-called endothelium-derived hyperpolarization (EDH) response Dalsgaard et al, 2010;Edwards et al, 2010;Köhler et al, 2010), SKA-31 was used as a pharmacologic tool to explore the role of K Ca channels in blood pressure regulation. While mice deficient in K Ca 3.1 and/or K Ca 2.3 exhibit impaired EDH responses and an increased mean arterial blood pressure (MAP) (Brahler et al, 2009), pharmacologic K Ca channel activation with SKA-31 lowered blood pressure in both mice and dogs (Sankaranarayanan et al, 2009;Damkjaer et al, 2012;Radtke et al, 2013). In dogs, i.v.…”

A Novel Pan-Negative-Gating Modulator of KCa2/3 Channels, Fluoro-Di-Benzoate, RA-2, Inhibits Endothelium-Derived Hyperpolarization–Type Relaxation in Coronary Artery and Produces Bradycardia In Vivo

“…Telemetry was performed as described previously (Brähler et al, 2009;Radtke et al, 2013 (Brähler et al, 2009) under deep anesthesia as described previously (Radtke et al, 2013). Mice were allowed to recover for 10 days until reaching normal day night rhythm.…”

“…Considering the patho-mechanistic roles of the channels, blockers of K Ca 3.1 channels have emerged as potential drug candidates for the treatment of sickle-cell disease (Ataga and Stocker, 2009), immunosuppression (Wulff and Castle, 2010), asthma (Van Der Velden et al, 2013), fibrosis , atherosclerosis (Toyama et al, 2008), and cancer (Ruggieri et al, 2012;D'Alessandro et al, 2013). Positive-gating modulators (activators) of K Ca 3.1, such as naphtho [1,2-d]thiazol-2-ylamine (SKA-31) (Sankaranarayanan et al, 2009) and 5-methylnaphtho [2,1-d]oxazol-2-amine (SKA-121) (Coleman et al, 2014), may improve endothelium-dependent vasodilation and lower blood pressure (Sankaranarayanan et al, 2009;Köhler et al, 2010;Damkjaer et al, 2012;Mishra et al, 2013;Radtke et al, 2013;Wulff and Köhler, 2013). Activators of K Ca 2 channels could be useful to treat epilepsy and ataxia (Shakkottai et al, 2011), while blockers may improve learning and memory.…”

Pharmacological gating modulation of small- and intermediate-conductance Ca2+-activated K+channels (KCa2.x and KCa3.1)

“…62,63 Mice deficient in K Ca 3.1 and/or K Ca 2.3 exhibit impaired EDH responses and show a~10 mmHg increase in mean arterial blood pressure, 28,29 while SKA-31 lowers blood pressure in normotensive and hypertensive mice as well as in conscious, normotensive dogs. 29,38,64 Since the blood pressure lowering effect of SKA-31 is absent in KCa3.1 ¡/¡ mice and higher doses of SKA-31 induce sedation and lower heart rate through central K Ca 2 channel activation, 65 it seems desirable to identify K Ca 3.1 selective positive gating modulators in order to help investigate whether such compounds could be developed into a new class of endothelial targeted antihypertensives. 63 This objective recently seems to have been achieved with the demonstration that the K Ca 3.1 selective SKA-121 lowers blood pressure in normotensive and hypertensive mice without affecting heart rate.…”